There is a need for new electrode materials with the capacity for lithium ions such that relatively higher energy densities can be realized. For example, work on improving graphite anodes in present-day batteries, which have a theoretical capacity of 372 mAh/g, and the current intercalcation cathode, such as LiCoO2, has identified several potential candidates.
In that regard, attention is directed to U.S. application Ser. No. 12/842,224 entitled “Silicon Clathrate Anodes For Lithium Ion Batteries” which among other things, was directed at electrodes comprising cage structures such as silicon clathrate particles.
The present disclosure now identifies beneficial attributes and utility of clathrate (Type I) allotropes of germanium and tin for relatively high-capacity anode or cathode materials which may find particular use in lithium type batteries.
Lithium-ion batteries are a family of rechargeable battery types in which lithium ions move from a negative electrode to the positive electrode during discharge, and back when charging. More specifically, during discharge, lithium ions Li+ carry current from the negative to the positive electrode through a non-aqueous electrolyte and separator diaphragm. The three primary functional components of the lithium-ion battery are therefore the anode, cathode and electrolyte.
Carbon or graphite has emerged as one of the most popular material for the anode. The cathode is generally one of three materials: a layered oxide (such as lithium cobalt oxide), a polyanion (such as lithium iron phosphate) or a spinel (such as magnesium oxide). Electrolytes may typically be selected from mixtures of organic carbonates such as ethylene carbonate or diethyl carbonate containing complexes of lithium ions.
Both the anode and cathode are therefore materials where the lithium may reversibly migrate. During insertion, lithium moves into the electrode. During extraction, lithium moves back out. The cathode half reaction may be written as:LiCoO2Li1−xCoO2+xLi++xe−The anode half reaction may be written as:xLi++xe−+6CLixC6 The overall reaction may be written as:Li++LiCoO2→Li2O+CoO
As noted above, there remains an ongoing need for higher specific capacity materials for higher energy density lithium-ion batteries. Work therefore continues on improving the carbon/graphite anode, which has a theoretical capacity of 372 mAh/g. However, the problems that are associated with finding a replacement material include identifying elements that, when participating in reversible reactions with lithium, do so in a manner that will not compromise anode performance.